Although petroleum and water are essentially immiscible, they often attain a condition of intimate and apparent permanent emulsification. A generally accepted theory to explain the unwillingness of the dispersed material to coalesce is the presence of a third substance, term an emulsifying agent. Minute particles of this "emulsifying agent" accumulate and are retained on the interface of the discontinuous phase by adsorption forces. The emulsifying agent may be either a finely divided colloidal substance insoluble in oil or water or a substance soluble in either the oil or the water. It is known that finely-divided solid substances such as clay will promote emulsification. Further, it is known that the liquid which preferentially wets the emulsifying agent will normally be the continuous phase of the emulsion. For example, finely-divided clay is wet more readily by water than by oil and will form oil-in-water emulsions whereas carbon black and oil-saturated clay are more readily wet by oil than by water and form water-in-oil emulsions. Similarly when soluble emulsifying agents are present, the liquid in which the emulsifying agent is more soluble will become the external phase. Sodium soaps, for example, are more soluble in water than in oil and thus form oil-in-water emulsions. On the other hand calcium soaps or asphaltic materials, being soluble in oil but not in water, form water-in-oil emulsions. Naturally occurring crude petroleum emulsions are commonly of the water-in-oil type though occasionally small quantities of the inverted type are encountered.
A known method of achieving separation of emulsions is by the use of coalescence, that is, flowing the emulsion through a medium arranged in such a way that droplets of the discontinuous phase tend to adhere to a coalescing material and then to each other, the droplets accumulating in size until they form globules which separate from emulsion. Once the emulsion is broken by the formation of the droplets and globules the oil can be skimmed off the surface of the emulsion for removal and the water from the emulsion can be removed from the lower portion of the vessel in which the emulsion is being treated.
One problem which has existed with cells for coalescing oil-water emulsions is that the fine mat material which is customarily utilized as the coalescing medium becomes clogged with solid particles in a relatively short time. Most emulsions which are encountered in the petroleum industry contain solid contaminants. When an attempt is made to coalesce the oil or water from the emulsion, depending on the type of emulsion, the coalescing cells function as filters and soon the porous passageways become filled with the solid contaminants.
It would be advantageous to have a coalescer material characterized by improved porosity while maintaining coalescing effectiveness so as to permit the passage of larger particles without becoming clogged as compared with other known types of coalescer materials.